Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) or laser ablation inductively coupled plasma optical emission spectrometry (LA-ICP-OES) techniques can be used to analyze the composition of a specimen (e.g., a solid or liquid specimen material). Often, a sample of the specimen is provided to an analysis system in the form of an aerosol (i.e., a suspension of solid and possibly liquid particles and/or vapor in a carrier gas, such as helium gas). The sample is typically produced by arranging the specimen within a laser ablation chamber (also referred to as a “specimen chamber”), introducing a flow of a carrier gas within the chamber, and ablating a portion of the specimen with one or more laser pulses to generate a plume containing particles and/or vapor, ejected or otherwise generated from the specimen (hereinafter referred to as “specimen material”), suspended within the carrier gas. Entrained within the flowing carrier gas, the specimen material is transported to an analysis system via a transport conduit to an inductively coupled plasma (ICP) torch where it is ionized. A plasma containing the ionized particles and/or vapor is then analyzed by an analysis system such as an mass spectrometry (MS) or optical emission spectrometry (OES) system.
As specimen chamber sizes for LA-ICP-MS and LA-ICP-OES increase, efficient collection of the specimen material becomes more desirable. A secondary volume (also referred to as a “sample cell, “sample capture cell,” or “cup”) is employed within the specimen chamber to localize extraction of the sample of the specimen material within the plume generated by the laser. There are two conventional methods for maintaining the secondary volume relative to a fixed location of the optical path of the laser pulses.
One method employs a noncontact magnetic coupling, through a window in the specimen chamber, between the secondary volume and a fixed reference magnet outside the specimen chamber. The secondary volume can be moved freely in two axes by means of a pair of precision bearing sliders. Flexible sample extraction tubing routes the sample from the secondary volume to the sample analysis system through a fixed location on a wall of the specimen chamber. Another method involves tracking the secondary volume relative to a fixed position by employing a fixed arm that slides through a rotatable piston seal in the wall of the specimen chamber. Both of these methods have advantages and disadvantages.